Cultured normal rat retinal pigment epithelium retains the capacity to phagocytize photoreceptor outer segments, whereas RCS rat pigment epithelium is deficient in this capacity. This experimental system will be used to study the mechanism of outer segment phagocytosis by the pigment epithelium. The interaction between the pigment epithelium and outer segments will be studied in both normal and RCS rat pigment epithelium by selectively modifying surface components of ourter segments and pigment epithelium and by varying the extracellular environment. The effects of inhibitors and stimulants of phagocytosis will be investigated. Experiments will be done to stimulate phagocytosis by RCS pigment epithelium. Should the specific defect in RCS rat pigment epithelium be found, the study will provide an important precedent for understanding an underlying cause of inherited retinal degeneration. Interactions between cultured neural retinal cell and pigment epithelium will also be studied. The role of the pigment epithelium in rhodopsin regeneration will be examined, using cultured pigment epithelium and isolated mammalian retinas.